(Anglais) Molecular mechanics and ab-initio calculations are performed in the framework of the interaction between the charged poly(ethylenedioxythiophene) (PEDOT), the p-toluensulphonic acid (TSA), and the diethylene glycol (DEG). Different possibilities of positioning the counterion along the conjugated polymer are studied. For each possibility (or orientation), the influence of relative position of the counterion on the stability of these charged interfaces is considered. The results indicate that the perpendicular orientation corresponds to the most stable structure of the PEDOT/TSA complex. The influence of the counterion on the charge distribution in the PEDOT is also investigated indicating that a strong influence of the interionic correlation on the stability of PEDOT by TSA. Further the packing of doped chains with their counterions is also determined. In the larger aggregates, the effect of the solvent is considered. These results give a new insight about the molecular arrangements of PEDOT/TSA interactions and allow to understand how charge transport along the stacks can take place.